What is it about?
Itis stated that without application of electric potential, the exposure time of 0.5– 1 min is quite enough for formation of predominantly single-layer graphene with minimum degree of defectiveness ID/IG = 0.27; Iit is shown that mainly single-layer graphene is formed on the substrate at negative potential U = −2 and −5 V, while at U = −2 V, practically defectiveness single-layer graphene with the size from 10 × 10 to 10 × 18 μm2 is formed; Iit is stated that at positive potential U = + 2 V on the substrate, formation of mainly single-layer graphene with minimum defectiveness ID/IG = 0.33 is observed.
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Why is it important?
Synthesis of single layer graphene with application electric field at low pressure in flame. The formation and further transformation of the PAH down to graphene and soot particles in the combustion of hydrocarbon fuels is a complex multistage process closely related to the overall kinetic combustion mechanism. The kinetic scheme of the combustion process includes the following main stages: (1) combustion of the initial fuel with the formation of acetylene; (2) formation of larger molecules and radicals and, ultimately, small aromatic molecules; (3) the growth of aromatic molecules due to the addition of acetylene molecules to them; (4) coagulation of PAH molecules and radicals; and (5) ionmolecular reactions (Gerasimov, 2009). Since benzene is used in our case, aromatic rings and the first small aromatic molecules are already present in the flame as intermediate products of benzene oxidation, which leads to acceleration of the process of further growth of small aromatic rings toward the formation of graphene. Further growth of the PAH to graphene, after the formation of the first aromatic ring, is associated with the interaction of aromatic radicals with acetylene molecules along the HACA mechanism (H-abstraction- C2H2-addition) (Whitesides & Frenklach 2010). In Prikhodko et al. (2014, 2015), results on the synthe
Perspectives
At present, production of large-scale domains of graphene (including single-layer graphene) with the area of at least more than 100 × 100 μm2 is an important task as the domains of this size are worth for practical commercial application. It is known that synthesis of large-scale graphene domains is not completely solved task. Therefore, development of new methods for synthesis of large-scale domains of graphene and improvement of the existing ones are very interesting and actual tasks in investigations of graphene.One of such methods is the method of synthesis of graphene layers in flame. The process of formation of nanostructures in flame (including those of graphene) is continuous, simple and is characterized by a quick reaction of, as a rule, 10–5–10–3 s. Investigations on synthesis of graphene in the flame at low pressure with the effect of electric field on a catalytic substrate are of a definite interest and fill in the gap in this field of knowledge. Synthesis of graphene at low pressure has advantages compared to synthesis at atmospheric pressure. They are (Tesner, 1979) as follows: combustion of hydrocarbon fuel at low pressure is characterized by a decreased soot formation process; the process of formation of carbon structures is preceded by formation of PAH; with the decrease in pressure, the thermal width of the flame front where the process of formation of PAH starts is more extended and uniform, approximately 5 mm, under the conditions of our experiment (the increase in the width of the flame front is approximately inversely proportional to pressure (Heydon, 1959); the rate of recombination of atoms decreases in connection with the decrease in the probability of collisions and the time between collisions of gas molecules increases, which contributes to an increase in the probability of the orientation of the particles correspondingly relative to each other (steric reaction factor) for the formation of graphene (Emmanuel & Knorre. 1984). Thus, all these create favorable conditions for synthesis of graphene layers.
Nikolay Prikhodko
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This page is a summary of: Synthesis of single-layer graphene in benzene–oxygen flame at low pressure, Combustion Science and Technology, June 2018, Taylor & Francis,
DOI: 10.1080/00102202.2018.1472588.
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